When I use DMA mode CY_U3P_DMA_TYPE_MANUAL_IN to transfer data from host computer to cyusb3014, will the data be overwritten if I do not call CyU3DmaChannelGetBuffer() in time? For example, I allocate 8 buffer for dma, and generate 9 OUT token, but I do not read data from any dma buffer. Will the 9th transaction data overwrite the 1st transaction data?

On the GPIF II side we've flags and on the USB side we've NRDY defined by USB specification which take care that packets are not lost. (Isochronous is the only transfer type which will run into data loss in your scenario but isochronous does come with the implied constraint that data loss will not affect the system).